I find the character of Calpurnia particularly interesting given her very interesting role as Scout and Jem's surrogate mother and as the person who also cares for Atticus in a way. She serves as both a caregiver and a disciplinarian and does quite a good job of demonstrating how to correct poor behavior and then be sure that you also demonstrate that you did it out of love and care for that person, not in an attempt to simply discipline them.

She also acts as a bridge between the two worlds and in particular helps Scout and Jem to realize that people in their lives have a role outside of the one they play for them. They get to see Calpurnia in church and realize that this other world is one they don't quite understand but that it exists and is important and valid and wonderful, just like theirs. This opening of their perspective is a wonderful example of how we can benefit from better understanding our friends and coworkers and neighbors.